The present invention relates to an acoustic apparatus such as a stereo acoustic system and a multi-channel acoustic system, to a method for determining a connection polarity of a speaker used in the acoustic apparatus, and to a recording medium having recorded thereon a program.
In content such as movies recorded on a DVD (Digital Versatile Disc) and in digital television broadcast, so-called multi-channel audio data, such as a 5.1 channel and a 7.1 channel, has come to be handled, and the number of chances of setting a multi-channel listening system, such as a 5.1 channel and a 7.1 channel, has increased.
For example, a listening system of a 5.1 channel is formed of six audio channels: a front left channel, a front center channel, a front right channel, a back left channel, a back right channel, and a subwoofer channel, and can play back audio by using six speakers corresponding to the six audio channels. The expression [0.1] in the 5.1 channel means a subwoofer channel compensating for low frequency components.
In a multi-channel listening system, at present, in a connection between at least one speaker and an amplifier section, two speaker cables, that is, + (positive) and − (negative) speaker cables, need to be connected to the + (positive) and − (negative) connection terminals of the amplifier unless a specifically dedicated socket section is provided; In this case, there are cases in which a user performs setting of polarities by mistake.
In this specification, the polarity related to the connection between an amplifier section and a speaker is referred to as a “connection polarity”. A case where a positive connection terminal and a positive cable are connected to each other, and a negative connection terminal and a negative cable are connected to each other, is referred to as a “positive connection (positive phase connection)”. In contrast to the above, a case where a positive connection terminal and a negative cable are connected to each other, and a negative connection terminal and a positive cable are connected to each other, is referred to as a “negative connection (reverse connection or reverse phase connection).
Some listening systems are designed to automatically detect a connection mistake of a speaker. For example, a measurement system capable of a determining a polarity related to the connection of a speaker shown in FIG. 8 (determining a connection polarity of a speaker) has been proposed. The measurement system shown in FIG. 8 allows a digital amplifier 102 to perform DAC (Digital-Analog Convert) playback of a signal for measuring a time-stretched pulse (TSP) (signal in which the energy of an impulse signal is distributed in a time axis), which is generated in a TSP signal generation section 101, and allows this signal to be emitted from a target speaker among speakers SP1 to SP5.
The TSP measurement signal emitted in this manner is collected by a microphone MC determined so as to be arranged, for example, at a position of 1 m in front in the tweeter axis of the target speaker. The TSP measurement signal is amplified and converted into a digital signal by a microphone amplifier+ADC (Analog-Digital Converter) 103. This signal is analyzed by a signal analysis section 104 in order to determine an impulse response. On the basis of a sign (+ (positive) or − (negative)) of the value of a rise point of a time waveform of the impulse response, the connection polarity of the speaker is determined.
As described above, a connection mistake of the speaker is detected, and the result is reported to the user so that, in the case of a connection mistake, a prompt for remaking the connection of that speaker can be made. As a result, also, in a multi-channel listening system, polarities of a speaker can be correctly connected to predetermined terminals of a digital amplifier, and a satisfactory audio listening environment can be arranged.
A technology used for emitting test sound from a speaker, for collecting this sound by a microphone arranged at a predetermined position, and for obtaining an impulse response as in the above-described listening system has been widely used to perform so-called time alignment in, for example, acoustic processing apparatuses disclosed in Japanese Unexamined Patent Application Publication Nos. 10-248097 and 10-248098 (to be described later). As a technology related to a polarity determination of a speaker, as disclosed in Japanese Unexamined Patent Application Publication No. 2000-102089, there is known a technology in which a user can perform determination of the polarity of the speaker on the basis of a difference in the sound localization of sound.
As is also described above, in a measurement system of the related art capable of making a determination as to the connection polarity of the speaker shown in FIG. 8, on the basis of the polarity (positive/negative) of the waveform of the rise of an impulse response, the determination of the connection polarity of the connected speaker is performed. However, in this case, the following problems may occur.
More specifically, a case in which a plurality of speaker units (devices) are installed in one speaker system and polarities of each unit inside the speaker system (internal unit polarities) are not aligned becomes a problem. In this case, the polarity of the rise may differ depending on the measurement point (the geometrical position of the microphone setting) of an impulse response, and the problem of incapable of performing an accurate polarity determination arises.
As one speaker system in which a plurality of speaker units are installed, there is a so-called 2-way type formed of a so-called woofer and a so-called tweeter. In terms of this 2-way type, when importance is given on the characteristics of coupling (cross-over) at the frequencies of the woofer and the tweeter, speaker units may be installed inside the speaker system (inside the housing) in a state in which the polarities of the two units are changed by a filter design and the phases are inverted.
In this specification, a speaker (device) of a single body, such as a woofer and a tweeter, is referred to as a “speaker unit”, and one or more speaker units installed inside one housing are referred to as a “speaker system” or simply as a “speaker”.
FIG. 9 shows examples of each impulse response when the position of a microphone MC is changed by using a speaker system SP in which the “internal unit polarity” of the woofer is in a positive phase connection (positive connection) and the “internal unit polarity” of the tweeter is in a reverse phase connection (reverse connection). When the “internal unit polarity” is in a positive phase connection, when a positive signal is input, the vibration plate of the speaker unit moves toward the front. When the “internal unit polarity” is in a reverse phase connection, when a positive signal is input, the vibration plate of the speaker unit moves toward the back.
As shown in part B of FIG. 9, when characteristics measurement and analysis are performed in such a manner that the microphone MC is arranged at a position nearly equal from the tweeter and the woofer and toward the front facing the sound emitting face of a speaker system SP, and an impulse signal (impulse sound) emitted from the speaker system SP is collected, an impulse response shown in a response waveform chart in part B of FIG. 9 is observed.
The impulse response of the speaker system SP may be considered as the addition of the two individual impulse responses of the woofer and the tweeter (including a network circuit). In general, since the energy of the woofer part is larger than that of the tweeter, the rise point of the impulse response waveform is in a positive direction. In the case of, for example, an ordinary listening environment, in particular, regarding the front speaker, the speaker unit is made to usually match the height at approximately the ear position of a listener, and the sign of the rise point of the impulse response near the speaker axis can be considered as the “connection polarity” of the speaker system.
However, when characteristics measurement and analysis of the speaker system are to be performed, if the position of the microphone with respect to the speaker system is strictly determined, only preparing a state in which characteristics of the speaker system can be measured accurately is hard. It is preferable that, if possible, the position of the microphone with respect to the speaker system has a degree of freedom so that it can be installed at a free position.
When the microphone is to be installed to measure and analyze the characteristics of the speaker system, when it is considered that a user can install it at a desired position and at a convenient position, the microphone is not necessarily installed toward the front in the speaker axis, as shown in part B of FIG. 9. For example, as shown in part A of FIG. 9, there is a case in which the microphone MC is installed at a position higher than the speaker system SP in such a manner as to be offset from the speaker axis, and also, as shown in part C of FIG. 9, there is a case in which the microphone MC is installed at a position lower than the speaker system SP.
Then, as shown in part A of FIG. 9, when the microphone MC is installed at a position higher than the speaker system SP, the tweeter becomes closer to the microphone MC when compared to the woofer. Furthermore, as shown in part C of FIG. 9, when the microphone MC is installed at a position lower than the speaker system SP, the woofer becomes closer to the microphone MC when compared to the tweeter.
In the case of the example shown in FIG. 9, each unit of the woofer and the tweeter is mounted side by side in the height direction of the speaker system SP. Therefore, in the case of examples shown in parts A and C of FIG. 9, the difference between the arrival times of the impulse signals from each unit becomes clear, and as shown in the response waveform of parts A and C of FIG. 9, an impulse response with respect to each unit appears clearly.
Then, as shown in part C of FIG. 9, when the position of the microphone MC is close to the unit (woofer in this case) that is in a positive phase connection inside the speaker SP, the connection polarity matches the rise polarity of the impulse response. However, the problem is a case shown in part A of FIG. 9. Even when the speaker connection of the user is correct, since the impulse signal emitted from the tweeter in which the internal unit polarity is in a reverse phase connection arrives the microphone MC earlier, it could be determined as being “reversely connected”.
This fact poses a serious problem due to the following reasons. In the listening system for a multi-channel, regarding, in particular, a small surround speaker, a case in which a microphone is installed in a wall or on a ceiling in a portion higher than the ear of the listener, and a case in which a microphone is installed on a floor due to the environment of the installation place can actually occur. Therefore, depending on the position of the microphone with respect to the speaker system, it is difficult to accurately make a determination as to whether or not the connection polarity of the speaker is correct on the basis of the determination of only the polarity of the rise of the impulse response.
In view of the above, it is desirable to reliably and quickly make a determination as to the connection polarity of a speaker without limiting the installation position of a microphone with respect to a speaker system.